Healthy Learning Environment Introduction: A major issue facing the construction industry today is creating a healthy learning environment for school buildings. Healthy learning environments are crucial for maximizing the students education, while minimizing potential short term and long term health problems. The United States Environmental Protection Agency (EPA) has conducted studies of human exposure to air pollutants. Those studies indicate that indoor levels of pollutants may be 2-5 times, and sometimes 100 times, higher than outdoor levels. This is a major concern, because it is estimated that most people spend about 90% of their time indoors. The EPA has also ranked indoor air pollution among the top five environmental health risks to the public. For this reason, it is important to incorporate natural ventilation into the building. Good indoor air quality contributes to a favorable learning environment for students, performance of teachers and staff, and a sense of comfort, health and well-being for all school occupants. These combine to assist a school in its core mission - educating children. - U.S. Environmental Agency Healthy learning environments are also effected by the amount and quality of the buildings lighting system. It is vastly important that there is sufficient indoor lighting in order to maximize the performance of the students as well as the teachers. Another important feature to consider is maximizing the amount of natural daylighting that enters the building. Studies have shown that the use of natural daylighting has improved test scores compared to electric lighting. With all of this knowledge, it is important that members of the construction industry work together to improve the indoor learning environment for the kids. Failure to look into this matter could result in the following consequences:
Increasing the potential for long term and short term health problems Negative impact on student learning environment and comfort level Increased absenteeism Reducing the performance of teachers and staff due to discomfort, sickness, or absenteeism Reducing the efficiency of the schools operating systems and equipment Increasing potential of temporary school closing Creating negative publicity that could damage school s image and effectiveness Creating potential liability problems Background: Indoor air quality is infected by polluted outdoor air, HVAC equipment, emissions from office equipment, building furnishings, as well as indoor sources such as odors and Volatile Organic Compounds (VOC s). VOC s are found in everyday items such as paints, coatings, and cleaning fluids. They have been found to be a major contributing factor to air pollution. VOC s are a public health hazard, causing asthma and permanent lung damage. It has been determined that controlling VOC s is an effective method for minimizing ozone levels and creating a healthier environment. HVAC equipment is a common source for microbiological growth, namely bacteria, mold, mildew, and fungi. Microorganisms like to grow in cool, dark, damp places. HVAC equipment is an ideal space for them to live, because of the amount of moisture content and condensation, as well as being a dark area. Below is a more detailed list of sources for indoor air pollutants:
Outside Sources Polluted Outdoor Air Pollen, dust, fungal spores Industrial emissions Vehicle emissions Nearby Sources Loading docks Odors from dumpsters Unsanitary debris or building exhausts near outdoor air intakes Underground Sources Radon Pesticides Leakage form underground storage tanks Components/Furnishings Components Microbiological growth on soiled or water damaged materials Dry taps that allow the passage of sewer gas Materials containing VOC's, inorganic compounds, or damaged asbestos Materials that produce particles or dust Furnishings Emissions from new furnishings and floorings Microbiological growth in soiled or water damaged furnishings Building Equipment HVAC Equipment Microbiological growth: Drip pans Ductwork Coils Humidifiers Improper venting of combustion products Dust or debris in ductwork Non-HVAC Equipment Emissions from office equipment Volatile Organic Compounds Ozone Emissions from shops, labs, cleaning processes Indoor Sources Science laboratories Vocational arts areas Copy/print areas Food prep areas Smoking lounges Cleaning materials Emissions from trash Pesticides Odors and VOC's from paint, chalk, and adhesives Occupants with communicable diseases Dry-erase markers and pens Insects and pests Personal care products
Problem Statement: An estimated 70% of all school buildings have indoor air quality problems, leading to an unhealthy environment. This is a greater concern for elementary school s, because children breathe a greater volume of air relative to their body weight compared to adults and can be more sensitive to indoor air pollution. Additionally, occupants of school buildings are closer together than office buildings, with approximately four times the occupant density. This poor indoor environment leads to a decrease in production out of the students as well as the teachers, and can lead to increased health risks. Until recently, air handlers and fan coil units were equipped with flat condensate drain pans. This design allows water to collect in stagnant pools, increasing the growth of mold and slime and increasing the likelihood of air-stream contamination. Also, the slime build up can clog the drain line and force condensate water to overflow into the bottom of the air handler or fan coil unit. That means more wet interior surfaces and more potential for mold growth. This increase is moisture content could also promote possible damage to the equipment and to the building. Solution: Implementing a healthy learning environment can be achieved by eliminating or reducing indoor air pollutants, regulating thermal comfort levels, and utilizing natural ventilation and daylighting. An easy and effective way to reduce indoor air pollutants is to attack the source. For microbial growth, the main source is the HVAC system. Three ways to control microbial growth are to use sloped drain pans, cleanable surfaces, and accessibility to all areas of the HVAC equipment. These methods will help reduce or eliminate the potential for microbial growth.
Accessibility is important in order to regulate cleaning, inspection, and maintenance of the equipment. Hinged doors or removable panels can be used on the HVAC equipment to allow accessibility. Also, there should be no exposed fiberglass insulation used, because it is more susceptible to absorbing moisture. Instead, closed-cell foam or foil-faced insulation should be used to eliminate the penetration of moisture. HVAC equipment should be cleaned regularly, keeping the system clean and dry to reduce the potential risk for microbial growth. Sloped condensate drain pans should be used on all HVAC equipment with cooling coils, preferably in two directions, to assure positive drainage and reducing microbial growth. The pans should also be constructed of high-quality stainless steel to resist corrosion and reduce premature leakage. Proper trapping of all drain connections is equally important to reduce the risk of drawing sewer gases into the air handler and distributing them throughout the building. Double-sloped and trapped condensate drain pan Regulating thermal comfort levels is a must for implementing a healthy learning environment. One way to regulate indoor thermal comfort levels is to use sensors in each room. Temperature and carbon dioxide should be regulated in each individual space.
The biggest factor in improving indoor air quality is humidity levels. Humidity should be regulated to between 40% - 50%. One method for reducing and controlling humidity would be installing a two wheel desiccant system. Desiccant systems are retrofits to the existing mechanical system. They are installed on the roof near the fresh air intake and connected with the existing HVAC system ventilator. The main goal of a two wheel desiccant system is to control humidity by controlling the amount of condensate with in the system. It accomplishes this feat by absorbing moisture from the outside air into the desiccant, which has a lower vapor pressure than the outside air. In order to vaporize the moisture, a direct-fire gas heater is used to heat the wheel. This creates a small set back, because the air is heated as it passes through the desiccant wheel. The new sensible air is then slightly cooled as it passes through a heat exchange wheel. Next the air is cooled down to supply air temperature before entering the space, by a cooling coil. The exhaust air leaving the room helps cool down the supply air which is entering the room through the heat exchange wheel. It then passes through the wet portion of the desiccant wheel and expels the moisture outside through the exhaust air. This process can better be seen in the diagram bellow.
Desiccant wheels have become a nice supplement to existing HVAC systems. They improve indoor air quality by lowering moisture and microbial growth in the mechanical system. Two wheel desiccant systems are priced around $5/cfm. The total cubic feet /minute of is 26,900 cfm. The desiccant wheel would cost around $134,500. Another way to eliminate moisture and possible microbial growth is to eliminate the source. is a dedicated outdoor air system with parallel fan coil units in each classroom. Each fan coil unit has a drip pan to collect condensate moisture. These drip pans are ideal homes for microbial growth. An alternative would be to use a dedicated outdoor air system with a parallel variable air volume (VAV) system. With a VAV system implemented, the fan coil units would be eliminated, which would eliminate the potential for microbial growth within the classroom. Instead of having drip pans in each fan coil unit in each classroom, there would only be one drip pan in the VAV system.
Microbial growth can also be eliminated by installing a UV light which kills the microorganisms. Healthy learning environments can also be improved by utilizing natural ventilation and daylighting. Natural ventilation and daylighting have proved to show increased production of the occupants as well as increasing comfort levels inside the building. Not only do they increase comfort levels, but natural ventilation and daylighting also decrease energy costs. School buildings typically have sufficient daylighting in most spaces, especially classrooms. They also typically use operable windows, which can be controlled by the occupants in each space. Conclusion: Improving indoor air quality is essential when creating a healthy learning environment. The comfort level of the occupants is very important in order to maximize their production and attendance. Optimizing natural ventilation and daylighting will improve the indoor learning environment and also reduce energy costs. Humidity is the leading cause of microbial growth and must be regulated. I recommend adding a two wheel desiccant system to control humidity levels and condensation within the mechanical system.